Traveling-wave tube with oscillation preventing and gain shaping means including an elongated lossy ceramic element



3,324,338 EVENTING AND GAIN SHAPING MEANS INGLUDING'AN ELONGATED LOSSYCERAMIC ELEMENT FilGd Feb. 24, 1964 J 95 L. M. WINSLOW TRAVELING-WAVETUBE WITH OSCILLATION PR 5 Sheets-Sheet l June 6, 1967 L. M. WINSLOW3,324,338

'I'RAVELINGWAVE TUBE WITH OSCILLATION PREVENTING AND GAIN SHAPING MEANSINCLUDING AN ELONGATED LOSSY CERAMIC EZEMENT Filed Feb. 24, 1964 3Sheets-Sheet 2 A I w W M 1 W M M M \& \Q\k\\nv\\v 5 a 5 a 5 J 2 2 M a -0L mm a w V m mm N e m ms M m w 1 M a me 4 m0 N 5 5 EH -4 z u a r MW w MM0 A7 ,4 d MM 7 -M w w w w ,0. a Q\H%\\ \m &

United States Patent 3,324,338 TRAVELING-WAVE TUBE WITH OSCILLATIONPREVENTING AND GAIN SHAPING MEANS INCLUDING AN ELONGATED LOSSY CERAM- ICELEMENT Lester M. Winslow, Los Augeles, Califi, assignor to HughesAircraft Company, Culver City, Calif., a corporation of Delaware FiledFeb. 24, 1964, Ser. No. 346,698 11 Claims. (Cl. 315-3.5)

ABSTRACT OF THE DISCLOSURE A longitudinally extending attenuatingtransmission line is disposed proximate to and externally of atravelingwave tube couple-d cavity slow-wave structure. The transmissionline may be a cylindrical lossy ceramic rod or a tubular lossy ceramicrod disposed coaxially about an electrically conductive rod. Thetransmission line is electromagnetically coupled to the slow-wavestructure via irises in the side walls of selected slow-wave structurecavities.

This invention relates generally to microwave devices, and moreparticularly relates to traveling-wave tubes having means forsubstantially eliminating oscillations at frequencies at the edges ofthe frequency passband of the tube, as well as for providing a carefullyshaped gain vs. frequency characteristic.

In traveling-wave tubes a stream of electrons is caused to interact witha propagating electromagnetic wave in a manner which amplifies theelectromagnetic energy. In order to achieve such interaction, theelectromagnetic wave is propagated along a slow-Wave structure, such asa conductive helix wound about the path of the electron stream or afolded waveguide type of structure in which a waveguide is effectivelywound back and forth across the path of the electrons. The slowwavestructure provides a path of propagation for the electromagnetic Wavewhich is considerably longer than the axial length of the structure, andhence, the traveling-wave may be made to effectively propagate at nearlythe velocity of the electron stream. The interactions between theelectrons in the stream and the traveling-wave cause velocitymodulations and bunching of the electrons in the stream. The not resultmay then be a transfer of energy from the electron beam to the wavetraveling along the slow-wave structure.

The present invention is primarily, although not necessarily, concernedwith traveling-Wave tubes utilizing slowwave structures of the coupledcavity, or interconnected cell, type. In this type of slow-wavestructure a series of interaction cells, or cavities, are disposedadjacent to each other sequentially along the axisof the tube. Theelectron stream passes through each interaction cell, andelectromagnetic coupling is provided between each cell and the electronstream. Each interaction cell is also coupled to an adjacent cell bymeans of a coupling hole at the end wall defining the cell. Generally,the coupling holes between adjacent cells are alternately disposed onopposite sides of the axis of the tube, although various otherarrangements for staggering the coupling holes are possible and havebeen employed. When the coupling holes are so arranged, a foldedwaveguide type of energy propagation results, with the traveling-waveenergy traversing the length of the tube by entering each interactioncell from one side, crossing the electron stream and then leaving thecell from the other side, thus traveling a sinuous, or serpentine,extended path.

One of the problems encountered in traveling-wave tubes of the coupledcavity variety, and especially high power tubes of this type, is atendency for the tube to oscillate at frequencies near the edges of thetube passband. This problem arises from the fact that for Wide bandoperation the phase velocity of the slow-wave circuit wave and thevelocity of the electron beam should be essentially synchronized over aslarge a range of frequencies as possible; hence, these velocities arealso close to synchronism near the upper and lower cutoff frequencies ofthe tube. Since the interaction impedance is high and thecircuit-to-transmission line match is poor at and in the vicinity of thecutoff frequencies, the loop gain for the tube, or even for a section ofthe tube, may be sufiiciently large for oscillations to start.

One technique which has been used to solve this oscillation probleminvolves coupling to the slow-Wave structure interaction cells speciallydesigned cavities which are sharply resonant at a frequency in thevicinity of a cutoff frequency of the slow-wave structure and providinglossy ceramic buttons in these special cavities in order to attenuateenergy at the resonant frequency of the cavity. While this technique isable to attenuate energy at those frequencies where the tube is mostlikely to oscillate without substantially affecting energy atfrequencies throughout the remainder of the tube passband, a minimumrefiection coefiicient is not provided. A low reflection coefficient ishighly desirable in preventing large fluctuations in gain as a functionof frequency at the low frequency end of the tube passband.

Accordingly, it is an object of the present invention to provide atraveling-Wave tube in which any tendency for the tube to oscillate inthe vicinity of the edges of the tube frequency passband issubstantially eliminated, and at the same time, in which a minimumreflection coefficient is provided to minimize small signal gainvariations at the low end of the frequency passband of the tube.

It is a further object of the present invention to provide a coupledcavity traveling-wave tube havinga readily controllable and carefullyshaped gain vs. frequency characteris-tic.

It is a still further object of the present invention to provide meansfor both suppressing oscillations and shaping the gain vs. frequencycharacteristic of a high power traveling-wave tube of the coupled cavitytype, and which means is simpler in design and requires fewer parts thanschemes heretofore employed.

In accordance with the foregoing objects, the traveling- Wave tube ofthe present invention includes means for providing a stream of electronsalong a predetermied path and a slow-wave structure having a pluralityof intercoupled interaction cavities disposed sequentially along andabout the electron stream path for propagating electromagnetic waveenergy in such manner that it interacts with the stream of electrons. Anattenuating transmission line including an elongated lossy ceramicelement is disposed proximate to and externally of the slow-wavestructure cavities, with the longitudinal axis of the lossy elementbeing parallel to the electron stream path. The lossy transmission linemay take the form of either a cylindrical rod of a mixture of ceramicand lossy materials, or a tubular rod of a lossy ceramic mixturedisposed coaxially about an electrically conductive rod. Coupling irisesin the side walls of at least certain ones of the slow-wave structureinteraction cavities provide electromagnetic coupling between theslow-wave structure and the lossy transmission line.

Additional objects, advantages and characteristic features of thepresent invention will become readily apparent from the followingdetailed description of a pre- .2 ferred embodiment of the inventionwhen taken in conjunction with the accompanying drawings in which:

FIG. 1 is an overall view partly in longitudinal section and partlybroken away of a traveling-wave tube constructed in accordance with thepresent invention;

FIG. 2 is a cross-sectional view taken along line 22 of FIG. 1;

FIG. 3 is a longitudinal sectional view taken along line 33 of FIG. 2;

FIG. 4 is a longitudinal section view taken along line 44 of FIG. 2; and

FIG. 5 is a series of graphs illustrating the percent signaltransmission as a function of frequency for the traveling-wave tube ofFIGS. 14, both with and without the attenuator rods of the presentinvention, as well as illustrating the loss vs. frequencycharacteristics of the attenuator rods.

Referring now to the drawings, and more particularly to FIG. 1, thereference numeral designates generally a traveling-wave tube whichincludes an arrangement 12 of magnets, pole pieces and spacer elementswhich will be described in detail later. At this point it should sufficeto state that the spacer elements and interior portions of the polepieces function as a slow-Wave structure, while the magnets and polepieces constitute a periodic focusing device for the electron beamtraversing the length of the slow-wave structure.

Coupled to the input end of the arrangement 12 is an input waveguidetransducer 14 which includes an impedance step transformer 16. A flange18 is provided for coupling the assembled traveling-wave tube 10 to anexternal waveguide or other microwave transmission line (not shown). Theconstruction of the flange 18 may include a microwave window (not shown)transparent to microwave energy but capable of maintaining a vacuumwithin the traveling-wave tube 10. At the out-put end of the arrangement12 an output transducer 20 is provided which is substantially similar tothe input transducer 14 and which includes an impedance step transformer22 and a coupling flange 24, which elements are similar to the elements16 and 18, respectively, of the input transducer 14. For vacuum pumpingor out-gassin g the travel ing-wave tube 10 during manufacture, adouble-ended pumping tube 26 is connected to both of the input andoutput waveguide transducers 14 and 20.

An electron gun 28 is disposed at one end of the traveling-wave tube 10which, although illustrated as the input end in FIG. 1, mayalternatively be the output end if a backward wave device is desired.The electron gun 28 functions to project a stream of electrons along theaxis of the tube 10 and may be of any conventional construction wellknown in the art. For details as to the construction of the gun 28reference is made to Patent N0. 2,985,791, entitled, PeriodicallyFocused Severed Traveling-Wave Tube, issued May 23, 1961 to D. J. Bateset al. and assigned to the assignee of the present invention and toPatent No. 2,936,393, entitled, Low Noise Traveling-Wave Tube, issuedMay 10, 1960, to M. R. Currie et al. and assigned to the assignee of thepresent invention.

At the output end of the traveling-wave tube 10 there is provided acooled collector structure 30 for collecting the electrons in thestream. The collector is conventional and may be of any form well knownin the art For details as to the construction of the collector,reference is made to the aforesaid Patent No. 2,985,791 and to PatentNo. 2,860,277, entitled Traveling-Wave Tube Collector Electrode, issuedNov. 11, 1958, to A. H. Iversen and assigned to the assignee of thepresent invention.

The construction of the slow-wave structure and magnetic focusing systemfor the traveling-wave tube 10 are illustrated in more detail in FIGS.2-4. A plurality of essentially annular disk-shaped focusing magnets 32are interposed between a plurality of ferromagnetic pole pieces 34. Asillustrated in FIG. 2, the magnets 32 may be diametrically split intotwo sections 32a and 32b for convenience during assembly of the tube.The ferromagnetic pole pieces 34 extend radially inwardly of the magnets32 to approximately the perimeter of the region adapted to contain theaxial electron stream. The individual pole pieces are constructed insuch a manner that a short drift tube, or ferrule, 36 is provided at theinner extremity of each pole piece. The drift tube 36 is in the form ofa cylindrical extension, or lip, protruding axially along the path ofthe electron stream from both surfaces of pole piece 34, i.e., in bothdirections normal to the plane of the pole piece 34. The drift tubes 36are provided with central and axially aligned apertures 38 to provide apassage for the flow of the electron beam. Adjacent ones of the drifttubes 36 are separated by a gap 40 which functions as a magnetic gap toprovide a focusing lens for the electron beam and also as an interactiongap in which energy exchange between the electron beam andtraveling-wave energy traversing the slow-wave structure occurs.

Disposed radially within each of the magnets 32 is a slow-wave circuitspacer element 42 of a conductive non-magnetic material such as copper.Each spacer element 42 has an annular portion of an outer diameteressentially equal to the inner diameter of the magnets 32 and a pair ofoppositely disposed ear portions 43 and 44 projecting outwardly from theannular portion. Each spacer element also defines a central cylindricalaperture 45 to provide space for a microwave interaction cell, orcavity, 46 which is defined by the inner lateral surface of the spacer42 and the walls of the two adjacent pole pieces 34 projecting inwardlyof the spacer element 42. The inner diameter of the spacer 42 determinesthe radial extent of the interaction cell 46, while the axial length ofthe spacer 42 determines the axial length of the cell 46.

For interconnecting adjacent interaction cavities 46 an off-centercoupling hole 48 is provided through each of the pole pieces 34 topermit the transfer of electromagnetic wave energy from cell to cell. Asis illustrated, the coupling holes 48 may be substantially kidney-shapedand may be alternately disposed apart with respect to the drift tubes36. It should be pointed out, however, that the coupling holes 48 may beof other shapes and may be staggered in various other arrangements, suchas those disclosed in Patent No. 3,010,047, entitled, Traveling-WaveTube, issued Nov. 21, 1961, to D. J. Bates and assigned to the assigneeof the present invention. In any event, it will be apparent that thespacer elements 42 and the portions of the pole pieces 34 projectinginwardly of the spacers 42 not only form an envelope for the tube, butalso constitute a slow-wave structure for propagating traveling-waveenergy in a serpentine path along the axially traveling electron streamso as to support energy exchange between the electrons of the stream andthe traveling-wave.

The axial length of the magnets 32, hence that of the spacers 42, isequal to the spacing between adjacent pole pieces 34, and the radialextent of the magnets 32 is approximately equal to or, as shown,slightly greater than that of the pole pieces 34. To provide focusinglenses in the gaps 40, the magnets 32 are stacked with alternatingpolarity along the axis of the tube, thus causing a reversal of themagnetic field at each magnetic lens and thereby providing a periodicfocusing device. It should be pointed out, however, that although thelengths of the spacers 42 may be substantially constant, they may alsobe varied slightly with respect to each other so that the effectiveaxial length of the cavities 46 is varied as a function of distancealong the tube to ensure that the desired interaction between theelectron stream and the traveling waves will continue to a maximumdegree even though the electrons are decelerated toward the collectorend of the tube.

As has been mentioned above, in prior art traveling Wave tubes of thetype described there may be a tendency for the tube to oscillate atfrequencies near the edges of the slow-wave circuit passband and for thegain to fluctuate excessively at the low frequency end of the passband.The present invention eliminates this tendency by coupling in parallelwith the slow-wave circuit at least one lossy transmission lineespecially designed to introduce relatively wide-band loss, and therebyshape the gain vs. frequency characteristic of the traveling-wave tube.

In one arrangement according to the present invention, best illustratedin FIGS. 2 and 4, a pair of such lossy transmission lines are utilized.The first transmission line comprises a solid cylindrical lossy ceramicrod 50 disposed on one side of the slow-wave circuit with itslongitudinal axis parallel to the electron beam path. The secondtransmission line comprises a coaxial arrangement 51 including a tubularlossy ceramic rod 52 coaxially disposed about an electrically conductiverod 54 on the opposite side of the slow-Wave structure from the rod 50,with the common axis of the rods 52 and 54 disposed parallel to theelectron beam axis. It is pointed out that it is not necessary to employthe particular arrangement shown, but rather either a single solid linesuch as 50, a single coaxial line such as 51, a pair of solid lines, ora pair of coaxial lines may alternatively be used.

In order to accommodate the solid rod 50, cylindrical holes 56 areprovided in the projecting ear portions 44 of certain successive ones ofthe slow-wave circuit spacer elements 42, and which holes are axiallyaligned with cylindrical holes 58 of the same diameter in the polepieces 34 lying between these spacer elements to provide a rod-receivingpassageway. Similarly, the tubular rod 52 is disposed in therod-receiving passageway defined by aligned cylindrical holes 60 and 62in the projecting ear portions 43 of these spacer elements and in theintermediate pole pieces 34, respectively.

The cylindrical rod 50 is of a diameter d which may be from essentially0.293 inch to essentially 0.360 inch, for example. The tubular rod 52has an outer diameter (1, which may be of the aforementioned values, andan inner diameter which may vary from essentially 0.150 inch toessentially 0.220 inch, for example. The solid rod 50 is coupled to theslow-Wave circuit interaction cavities 45 by means of couplingpassageways, or irises, 63 of width i between the rod-receiving holes 56and the central apertures 45 of the respective spacer elements 42.Similarly, coupling irises 64 of Width i between the rod-receiving holes60 and the central apertures 45 of the respective spacers 42 function tocouple the coaxial line 51 to the slow-wave circuit interactioncavities. The width i of the irises 63 and 64 may be of a valueessentially between 0.100 and 0.250 inch, for example. A material whichmay be used for the rods 50 and 52 is a mixture of forsterite andsilicon carbide, with the percentage of silicon carbide varying fromessentially to essentially 60% for the solid rod 50 and from essentially20% to essentially 60% for the tubular rod 52. Other materials whichcould be used are silicon carbide and alumina, silicon carbide and talc,or other ceramic and lossy material combinations.

It should be apparent that the exact values of the dimensions (1, c, andi and the relative amounts of ceramic and lossy materials to be usedwill depend upon the frequencies at which loss is to be introduced andthe particular shape desired for the transmission vs. frequencycharacteristic of the slow-wave structure, taking into account thedielectric constant e of the lossy ceramic mixture. In general, thegreater the percentage of silicon carbide and the greater the diameterd, the greater the amount of loss that will be introduced. Increasingthe inner diameter c of the tubular rod will generally decrease theloss, while increasing the iris width i will tend to increase the losson account of increased coupling to the lossy transmission line,although care should be taken that the iris reflection coefficient isnot increased excessively. Preferably, the solid transmission line 50 isdesigned to introduce loss around the high frequency end of theslow-wave circuit frequency passband, and the coaxial transmission line51 provides the desired loss in the low frequency region, although withproper design either type of line can provide loss at either end of theslowwave circuit passband.

An example of a particular oscillation suppression and gain shapingarrangement which has been constructed in accordance with the presentinvention will now be given. In this arrangement, which takes theparticular configuration illustrated in FIGS. 2 and 4, the attenuatorrods 50 and 52 both extend longitudinally along the slow-wave structurethroughout eighteen of the interaction cavities 46. For the ninecavities nearest the input (electron gun) end of the structure, thediameter d for both the rods 50 and 52 was 0.293 inch, with an innerdiameter 0 for the tubular rod 52 of 0.160 inch; the widths i for theirises 63 and 64 were 0.250 and 0.205 inch, respectively; the solid rod50 and the tubular rod 52 contained, respectively, 5% and 60% siliconcarbide with the remainder forsterite. For the nine cavities nearest theoutput (collector) end of the structure, the widths i for the respectiveirises 63 and 64 were 0.205 and 0.235 inch; the percentage of siliconcarbide in the hollow rod 52 was reduced to 20%, with the percentage ofsilicon carbide in the solid rod 50 and the dimensions d and 0 remainingthe same a those given above with respect to the section nearer theinput end of the tube.

The results afforded by the present invention toward eliminatingoscillations and providing a carefully shaped gain vs. frequencycharacteristic with vastly reduced gain fluctuations may be betterappreciated 'by making reference to FIG. 5. In this figure the curve 70illustrates the percent transmission as a function of frequency for thetraveling-Wave tube shown in FIGS. 1-4 but without the inclusion of thelossy transmission lines 50 and 51. From this curve it may be noticedthat extreme fluctuations in percent transmission occur essentiallybetween 7.3 and 7.7 gc. at the low end of the frequency passband andessentially between 10.7 and 11.1 gc. at the high end of the passband.

The transmission vs. frequency characteristics for the traveling-wavetube of FIGS. l-4 including lossy transmission lines 50 and 51 of theparticular compositions and dimensions set forth in the foregoingexample is depicted by the curve 72 of FIG. 5, with the attenuation indb afforded by this arrangement being shown in the curve 74. Starting atthe lower end of the frequency passband note that as the frequency isincreased, the transmission undergoes a smooth gradual increase fromZero up to a maximum value at around 10.0 gc., and then smoothlydecreases much more rapidly back to zero at the upper end of thepassband. Although some loss is introduced throughout the entirepassband (and the maximum transmission is only of its value absent thelossy transmission lines), the vast fluctuations in signal transmissionnear both the high and low extremeties of the slow-Wave circuit passbandhave been completely eliminated, thereby materially reducing thetendency toward oscillations in these frequency regions. In addition,the attenuator arrangement of the present invention provides a minimumreflection coefficient at the low end of the frequency passband,alfording a reduction in small signal gain variations.

It is pointed out that while the curve 72 of FIG. 5 shows the generalnature of the transmission vs. frequency properties of a traveling-wavetube slow-Wave structure according to the present invention, variationsin the shape of this transmission curve may be afforded by altering theconfiguration (i.e., whether solid or tubular rods) of the lossytransmission lines, as well as by changing the composition anddimensions of the rods 50 and 52 and the width of the irises 63 and 64in the manner pointed out above. Since the gain of a traveling-wave tubeis a function of its signal transmission and loss properties, a readilycontrollable and carefully shaped gain vs. frequency characteristic isthus afforded.

Although the present invention has been shown and described with respectto specific embodiments, nevertheless various changes and modificationsobvious to one skilled in the art to which the invention pertains aredeemed to be within the spirit, scope and contemplation of the inventionas set forth in the appended claims.

What is claimed is:

1. A traveling-wave tube comprising: means for providing a stream ofelectrons along a predetermined path, slow-wave structure means defininga plurality of intercoupled interaction cavities disposed sequentiallyalong and about said predetermined path for propagating electromagneticwave energy in such manner that it interacts with said stream ofelectrons, an elongated lossy ceramic element disposed proximate to andexternally of said slowwave structure means with the longitudinal axisof said element parallel to said predetermined path, and said lossyceramic element being electromagnetically coupled to a plurality of saidinteraction cavities.

2. A traveling-wave tube according to claim 1 wherein said lossy ceramicelement comprises a mixture of silicon carbide and a material selectedfrom the group consisting of forsterite, alumina, and talc, with thepercentage of silicon carbide varying from essentially 5% to essentially60%.

3. A traveling-wave tube comprising: means for providing a stream ofelectrons along a predetermined path, slow-wave structure means defininga plurality of intercou-pled interaction cavities dis-posed sequentiallyalong and about said predetermined path for propagating electromagneticWave energy in such manner that it interacts with said stream ofelectrons, a cylindrical rod of a mixture of ceramic and lossy materialsdisposed proximate to and externally of said slow-wave structure meanswith the longitudinal axis of said rod parallel to said predeterminedpath, and said slow-wave structure means further defining a plurality ofirises coupling selected ones of said interaction cavities to saidcylindrical rod.

4. A traveling-wave tube comprising: means for providing a stream ofelectrons along a predetermined path, slow-wave structure means defininga plurality of inter coupled interaction cavities disposed sequentiallyalong and about said predetermined path for propagating electromagneticwave energy in such manner that it interacts with said stream ofelectrons, a tubular rod of a mixture of ceramic and lossy materialsdisposed proximate to and externally of said slow-wave structure meanswith the longitudinal axis of said rod parallel to said predeterminedpath, an electrically conductive rod coaxially disposed within saidtubular rod, and said slow-wave structure means further defining aplurality of irises coupling selected ones of said interaction cavitiesto said tubular rod.

5. A traveling-wave tube comprising: means for providing a stream ofelectrons along a predetermined path, slow-wave structure means defininga plurality of intercoupled interaction cavities dis-posed sequentiallyalong and about said predetermined path for propagating electromagneticwave energy in such manner that it interacts with said stream ofelectrons, a cylindrical rod of a mixture of ceramic and lossy materialsdisposed proximate to and externally of said slow-wave structure meansalong one side thereof with the longitudinal axis of said cylindricalrod parallel to said predetermined path, a tubular rod of a mixture ofceramic and lossy materials disposed proximate to and externally of saidslow-wave structure means along the opposite side thereof with thelongitudinal axis of said tubular rod parallel to said predeterminedpath, an electrically conductive rod coaxially disposed within saidtubular rod, and said slow-wave structure means further defining aplurality of irises coupling selected ones of said interaction cavitiesto said cylindrical rod and said tubular rod.

6. A slow-wave structure for promoting interaction between a stream ofelectrons projected along a predetermined path and an electromagneticwave comprising: a plurality of axially aligned essentially annularelectrically conductive spacer elements sequentially disposed along andencompassing said predetermined path, a plurality of electricallyconductive plates each mounted between a pair of adjacent spacerelements to define in conjunction with said spacer elements a pluralityof interaction cavities, said plates defining aligned apertures in theircentral regions to provide a passage for said electron stream andfurther defining coupling holes in regions readily outwardly of saidcentral regions for interconnecting adjacent interaction cavitieswhereby a propagation path is provided for said electromagnetic wave ina manner to provide interaction between said electron stream and saidelectromagnetic wave, at least certain successive ones of said spacerelements and plates defining aligned cylindrical apertures to provide apassageway parallel to said predetermined path, a cylindrical rod of amixture of ceramic and lossy materials disposed within said passageway,and each of said certain ones of said spacer elements further defining apassageway between the interaction cavity and the rod-receiving aperturedefined thereby.

7. A slow-wave structure for promoting interaction between a stream ofelectrons projected along a predetermined path and an electromagneticwave comprising: a plurality of axially aligned essentially annularelectrically conductive spacer elements sequentially disposed along andencompassing said predetermined path, a plurality of electricallyconductive plates each mounted between a pair of adjacent spacerelements to define in conjunction with said spacer elements a pluralityof interaction cavities, said plates defining aligned apertures in theircentral regions to provide a passage for said electron stream andfurther defining coupling holes in regions radially outwardly of saidcentral regions for interconnecting adjacent interaction cavitieswhereby a propagation path i provided for said electromagnetic wave in amanner to provide interaction between said electron stream and saidelectromagnetic wave, at least certain successive ones of said spacerelements and plates defining aligned cylindrical apertures to provide apassageway parallel to said predetermined path, a tubular rod of amixture of ceramic and lossy materials disposed Within said passageway,an electrically conductive rod coaxially disposed within said tubularrod, and each of said certain ones of said spacer elements furtherdefining a passageway between the interaction cavity and therod-receiving aperture defined thereby.

8. A slow-wave structure for promoting interaction between a stream ofelectrons projected alOng a predetermined path and an electromagneticwave comprising: a plurality of axially aligned essentially annularelectrically conductive spacer elements sequentially disposed along andencompassing said predetermined path, a plurality of electricallyconductive plates each mounted between a pair of adjacent spacerelements to define in conjunction with said spacer elements a pluralityof interaction cavities, said plates defining aligned apertures in theircentral regions to provide a passage for said electron stream andfurther defining coupling holes in regions radially outwardly of saidcentral regions for interconnecting adjacent interaction cavitieswhereby a propagation path is provided for said electromagnetic wave ina manner to provide interaction between said electron stream and saidelectromagnetic wave, at least certain successive ones of said spacerelement-s and plates defining a first and a second series of alignedcylindrical apertures on opposite sides of said interaction cavities toprovide a first passageway parallel to said predetermined path on oneside of said interaction cavities and a second passageway parallel tosaid predetermined path on the opposite side of said interactioncavities, a cylindrical rod of a mixture of ceramic and lossy materialsdisposed within said first passageway, a tubular rod of a mixture ofceramic and lossy materials 9 disposed within said second passageway, anelectrically conductive rod coaxially disposed within said tubular rod,and each of said certain ones of said spacer elements further definingfirst and second irises between the interaction cavity and therespective first and second rod-receiving apertures defined thereby.

9. An arrangement for focussing a stream of electrons along apredetermined path and for promoting interaction between said stream ofelectrons and an electromagnetic wave comprising: a plurality of axiallyalinged essentially annular magnets, a plurality of ferromagnetic polepieces interposed between and abutting adjacent magnets, a hollowessentially cylindrical nonmagnetic spacer element having an outerdiameter essentially equal to the inner diameter of said essentiallyannular magnets disposed within each of said magnets, said pole piecesprojecting internally of said spacer elements to define therewith aplurality of interaction cavities, said pole pieces defining alignedapertures in their central regions to provide a passage for saidelectron stream and further defining coupling holes in regions readilyoutwardly of said central regions for interconnecting adjacent cavitieswhereby a propagation path is provided for said electromagnetic wave ina manner to provide interaction between said electron stream and saidelectromagnetic wave, at least certain successive ones of said spacerelements each defining at least one outwardly extending ear portion,said ear portions and each pole piece disposed between said certain onesof said spacer elements defining aligned cylindrical apertures toproivde a passageway parallel to said predetermined path, a cylindricalrod of a mixture of ceramic and lossy materials disposed within saidpassageway, and each of said certain ones of said spacer elementsfurther defining a passageway between the interaction cavity androd-receiving aperture defined thereby.

10. An arrangement for focusing a stream of electrons along apredetermined path and for promoting interaction between said stream ofelectrons and an electromagnetic wave comprising: a plurality of axiallyaligned essentially annular magnets, a plurality of ferromagnetic polepieces interposed between and abutting adjacent magnets, a hol lowessentially cylindrical nonmagnetic spacer element having an outerdiameter essentially equal to the inner diameter of said essentiallyannular magnets disposed within each of said magnets, said pole piecesprojecting internally of said spacer elements to define therewith aplurality of interaction cavities, said pole pieces defining alignedapertures in their central regions to provide a passage for saidelectron stream and further defining coupling holes in regions readilyoutwardly of said central regions for interconnecting adjacent cavitieswhereby a propagation path is provided for said electromagnetic wave ina manner to provide interaction between said electron stream and saidelectromagnetic wave, at least certain successive ones of said spacerelements each defining at least one outwardly extending ear portion,said ear portions and each pole piece disposed between said certain onesof said spacer elements defining aligned cylindrical apertures toprovide a passageway parallel to said predetermined path, a tubular rodof a mixture of ceramic and lossy materials disposed within saidpassageway, an electrically conductive rod coaxially disposed withinsaid tubular rod, and each of said certain ones of said spacer elementsfurther defining a passageway between the interaction cavity and therod-receiving aperture defined thereby.

11. An arrangement for focusing a stream of electrons along apredetermined path and for promoting interaction between said stream ofelectrons and an electromagnetic wave comprising: a plurality of axiallyaligned essentially annular magnets, a plurality of ferromagnetic polepieces interposed between and abutting adjacent magnets, a hollowessentially cylindrical nonmagnetic spacer element having an outerdiameter essentially equal to the inner diameter of said essentiallyannular magnets disposed within each of said magnets, said pole piecesprojecting internally of said spacer elements to define therewith aplurality of interaction cavities, said pole pieces defining alignedapertures in their central regions to provide a passage for saidelectron stream and further defining coupling holes in regions readilyoutwardly of said central regions for interconnecting adjacent cavitieswhereby a propagation path is provided for said electromagnetic wave ina manner to provide interaction between said electron stream and saidelectromagnetic wave, at least certain successive ones of said spacerelements each defining first and second car portions extending outwardlyfrom opposite sides of said spacer element, said first ear portions andeach pole piece disposed between said certain ones of said spacerelements defining a first series of aligned cylindrical apertures toprovide a first passageway parallel to said predetermined path on oneside of said interaction cavities, said second ear portions and eachpole piece disposed between said certain ones of said spacer elementsdefining a second series of aligned cylindrical apertures to provide asecond passageway parallel to said predetermined path on the oppositeside of said interaction cavities, a cylindrical rod of a mixture ofceramic and lossy materials disposed within said first passageway, atubular rod of a mixture of ceramic and lossy materials disposed withinsaid second passageway, an electrically conductive rod coaxiallydisposed within said tubular rod, and each of said certain ones of saidspacer elements further defining first and second irises between theinteraction cavity and the respective first and second rod-receivingapertures defined thereby.

N 0 references cited.

HERMAN KARL SAALBACH, Primary Examiner.

P. L. GENSLER, Assistant Examiner.

1. A TRAVELING-WAVE TUBE COMPRISING: MEANS FOR PROVIDING A STREAM OFELECTRONS ALONG A PREDETERMINED PATH, SLOW-WAVE STRUCTURE MEANS DEFININGA PLURALITY OF INTERCOUPLED INTERACTION CAVITIES DISPOSED SEQUENTIALLYALONG AND ABOUT SAID PREDETERMINED PATH FOR PROPAGATING ELECTROMAGNETICWAVE ENERGY IN SUCH MANNER THAT IT INTERACTS WITH SAID STREAM OFELECTRONS, AN ELONGATED LOSSY CERAMIC ELEMENT DISPOSED PROXIMATE TO ANEXTERNALLY OF SAID SLOWWAVE STRUCTURE MEANS WITH THE LONGITUDINAL AXISOF SAID ELEMENT PARALLEL TO SAID PREDETERMINED PATH, AND SAID LOSSY